The medical device industry produces a wide variety of electronic devices for treating patient medical conditions. Depending upon the medical condition, medical devices can be surgically implanted or connected externally to the patient receiving treatment. Medical professionals or other clinicians use medical devices alone or in combination with drug therapies and surgery to treat patient medical conditions. For some medical conditions, medical devices provide the best, and sometimes the only, therapy to restore an individual to a more healthful condition and a fuller life. Examples of implantable medical devices designed to deliver therapeutic electrical stimulation include neurological stimulators, pacemakers, defibrillators and drug pumps. Most implantable medical devices are powered by an internal battery or other power source associated with or internal to the device.
Because surgery is required to implant most implantable medical devices, it is desirable, particularly in devices that consume power quickly, to make the internal battery rechargeable. An external power source may then be used to recharge the rechargeable battery, commonly transcutaneously via an inductive link between an external coil and an internal coil. Depending on the nature of the implantable medical device and rechargeable battery in question, several hours will commonly be required to fully recharge the rechargeable battery. While some implantable medical devices may be able to delivery therapy to a patient for months or years on a single charge of a primary, non-rechargeable battery, some devices, particularly those that rely on a rechargeable power source or that deliver a relatively large amount of therapy constantly, may consume most of their charge in a matter of days or weeks.
Commonly, in order to recharge their implantable medical device, patients may sit in close proximity of their external charger, maintaining a recharging head, or the entire device, nearby or within a few inches of their implantable medical device. The rechargeable battery will commonly require several hours to charge from a relatively low amount of charge to a full or nearly-full level of charge. It is known in the art to provide patients with information pertaining to an estimated time to fully charge a rechargeable battery.
U.S. Pat. No. 6,928,372, Pozsgay et al., discloses a method for determining time to completion for a battery charging system. The system preferably includes a charger having a microprocessor and a battery with a memory. The memory includes information about the battery, including battery identifiers, charging state, charging procedures and charging termination information. The charger reads this battery and then determines the charging states associated with the battery. The charger then determines the present state of charge and calculates a time to completion for that state. The charger then determines times to completion for the remaining charge states, optionally compensating for self discharge within the battery. A total time to completion is determined by summing the times to completion for the respective charging states.